1. Field of the Invention:
The invention relates to circuit interrupters and, more particularly, to low friction latch mechanisms.
2. Description of the Prior Art:
Circuit breakers are widely used in industrial, commercial and residential applications to provide protection for electrical apparatus and distribution circuits powering the apparatus. Stored energy operating mechanisms are usually included in such circuit interrupters to latch the contacts in the closed position during normal operation. Overload currents flowing through circuits powering the electrical apparatus are detected by various forms of current sensing devices which actuate mechanisms to release the circuit breaker latch, thereby allowing the energy stored in the operating mechanism to open the contacts of the circuit breaker and interrupt the overload current flowing through the circuit. Usually, such overload currents cause a latching surface to slide upon a latch member until the latch member is released. However, friction between the latch member and the latching surface can reduce the sensitivity and accuracy of the circuit breaker in tripping at a predetermined overload current level. It is therefore desirable to minimize friction between the latch member and latching surface.
Since circuit breakers are manufactured in high volume, it is also desirable to reduce the cost of production by stamping the various parts of the circuit breaker mechanism from sheet metal. Such a stamping operation produces a sheared surface having a smooth portion and a rough portion. The smooth portion is formed during the initial stages of the stamping operation wherein the tool performs a combination of stretching and shearing. During later stages of the stamping operation, the sheet metal is torn by the tool, thereby producing the rough surface. In order to reduce latch friction produced by this rough surface, prior art circuit breaker latching surface were smoothed with a machining operation. While this satisfactorily reduced the friction of the latching surface, it increased the cost of the circuit breaker. It would be desirable to provide a latching surface having a low-friction area of contact between the latching surface and the corresponding latch member which does not require a machining operation.